1. Field of the Invention
The present invention relates to a displacement sensor that comprises magnetic sensing devices such as Hall ICs, and a magnetic member that generates a magnetic field and is movable relative to the magnetic sensing devices, the displacement sensor outputting electrical signals from the magnetic sensing devices having a level corresponding to the amount of displacement of the magnetic member.
2. Description of the Related Art
A displacement sensor disclosed in Japanese Patent Application Laid-open No. 2000-258109 has a rod-shaped magnetic member (e.g. a magnet) joined to a mover, and two magnetic sensing devices are disposed in positions differing by 180° on the same circumference centered on a central axis of the magnetic member. Output signals from the two magnetic sensing devices are averaged, whereby errors in the output signals from the two magnetic sensing devices due to misalignment of the rod-shaped magnet in the radial direction cancel each other out, and hence the accuracy of position detection is improved.
With such a displacement sensor, it is generally desired to expand the range of amounts of displacement that can be detected (the detection range).
Moreover, the installation position of the magnetic member may be slightly misaligned from the proper position. This misalignment comprises two components, a shift in the central axis of the magnetic member in the radial direction from the proper position of the axis, and a tilt of the central axis of the magnetic member from the proper direction of the axis; in general, such a shift and tilt are present compounded together. Errors occur in the output signals from the magnetic sensing devices due to this shift and tilt. It is desirable for errors due to such misalignment to be detected when the displacement sensor is shipped out from the factory, during use or the like, and for the displacement sensor to be calibrated based on this. However, with the prior art described above, the errors in the output signals from the magnetic sensing devices cannot be detected in the case that a shift and tilt of the magnetic member are compounded together.